[p2p-hackers] Morpheus, Freenet, MojoNation (was Semantic Routing BOF)

Steven Hazel sah at thalassocracy.org
Wed Aug 29 12:37:02 UTC 2001


Gordon Mohr <gojomo at usa.net> writes:

> Sometimes the Freenet docs talk about a "Progressive CHK" that is
> not the full-file SHA1.
> 
> Are some CHKs full-file SHA1 values, and others progressive
> (reverse-4k-blocks-in-a-maximally-lopsided-tree)?

Yes.  (Although the 4k block size isn't fixed.)

> If so, how does one tell the difference between the two kinds?

One requests the file.  The DataReply will have header information
that indicates which kind it is (PartSize and DataLength).  Every
document larger than the part size will be progressively hashed.

The purpose of this is to make it possible for nodes to periodically
verify that they're not being fed bunk data, rather than forcing them
to wait for the entire file before they can verify that it's what they
requested.

Incidentally, Brandon Wiley and I will be teaching a "Programming
Freenet" tutorial at the upcoming O'Reilly P2P and Web Services
conference, and I'll be covering this kind of thing in depth there:

http://conferences.oreillynet.com/cs/p2pweb2001/view/e_sess/1830

If you're interested, please do sign up, as they're probably going to
cancel the tutorial if we don't get more students soon.

--Steven



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